1. Field of the Invention
The present invention generally relates to techniques for authenticating digital images, and in particular to techniques for encoding authentication information and distributing that information throughout the image.
2. Background Description
Digital cameras offer high-resolution immediate imagery which can be processed and transmitted electronically without the need for scanning and digitizing a hard copy photograph. The digital nature of the resulting imagery, however, makes it more vulnerable to undetected manipulation in whole or in part. Where the imagery has evidentiary use, it is essential to incorporate a technique by which to determine that an image has not been altered.
Since it is often essential to know the precise date, time, and location where the image was taken, what imaging device was used, and who took the image, the apparatus and method of the present invention use an encoding of that information distributed throughout the image as a secure means of providing that information as well as a certificate of originality.
The method and apparatus of the present invention does not require the use of flash correlation. However, that technique provides a computationally simple and therefore rapid capability for decoding the two-dimensional encodings of data which provide authentication. Furthermore, flash correlation is fast enough to exhaustively consider all possibilities when certain encoded information is unknown, such as the ID of the specific camera used, the ID of the user, or the frame number or exact time of day a given image was taken. Alternately, steganography can be used.
Presence of a flash correlation artifact (FCA) between a Resultant Image and an encrypted representation of the Encoded Data Array is sufficient to identify its date/time, location, and source. Each of those values can be separately identified, or all can be simultaneously verified. Presence of an FCA between a Resultant Image and an Encrypted version of the Original Image indicates that the Resultant Image is authentic, It is not necessary to decrypt the Resultant Image or to perform pixel by pixel comparison in order to authenticate the image. Authentication of an image can be performed in one operation, regardless of the complexity of the image.
Confirmation of the camera ID, the date/time, and the location can be separately made, with or without being cued by annotation on the image.
Multi-colored or multi-grey level images can be similarly authenticated. Their complement is created by inversion of the grey scale or color chart. Alternately, colored images can be broken into components and represented by three layers of grey scale values, each of which is separately encoded and encrypted.